I was thinking I need some free float handguards for some of my rifles, most of which don't currently have them. The prices are all over the place - it looks like they run from $20 to $300+ Maybe even more ridiculous, I was interested in a Knight's Armament carbine handguard, which isn't even a free float system, and people seem to be selling those for about $300 each, used. WTF? To save time, I am mainly interested in straight Picatinny rail systems - not so much the M-lock and keymod and such. Somebody tell me, especially for the free float ones, what features make the expensive ones worth so much more?